This invention relates generally to a mechanism for deadlocking a door member to a door frame member in such manner as to accommodate sudden opening of the door member as by sudden pushing of an associated panic bar. More particularly, it concerns an external installation and fitting of mechanism, such as a temperature-responsive mechanism, that prevents opening of the door in case of fire.
Safety exit doors are widely used, and they commonly incorporate lock mechanisms which lock the doors to door frames, and which are releasable by operation of panic bars. See U.S. Pat. Nos. 1,638,748; 4,130,306; 4,083,590; and 4,368,905. U.S. Pat. No. 4,838,587 to Choi discloses an improved mechanism for controllably deadlocking a door to a door frame, for panic release.
There is need for simple, compact, reliable mechanisms of this type, which are readily installable externally upon such doors, using elongated actuator links installable within such doors, to thereby provide safety exit door operation, and which also block opening of the exit door in case of fire. There is also need for deadlocking mechanisms wherein only one latch and its operating rod are needed on a door, as adjacent the door top.